The MEMS (Micro Electro Mechanical System) switch is a mechanical switch that switches ON/OFF by physical contact, and the main characteristics of the MEMS switch are having isolation properties, linearity, and pressure resistance, which are higher than those of a semiconductor switch.
The electrostatic driving MEMS switch gives a potential difference between a movable electrode and a fixed electrode, drives an actuator by an electrostatic attractive force, and causes the switch to be in an ON-state by causing contact points to be in contact with each other. In order to turn off the switch, typically, the potential difference between electrodes is made zero and the contact points are separated by returning the electrodes to the respective original positions with a restoring force of a return spring.
The switching time, which is the main characteristic of the switching-type switch, is determined by an operation time in which the switch is changed from an OFF-state to an ON-state and a return time in which the switch is changed from an ON-state to an OFF-state. The operation time of the switch is changed by a potential difference, the facing area of the electrode, a spring constant of the return spring, and the distance of movement of the contact points, which are in contact with each other by the movement. In order to shorten the operation time, it only needs to soften the spring, and increase the potential difference and the electrode area. On the other hand, the return time of the switch is changed by a spring constant of the return spring and adhesion of the contact points. In order to shorten the return time, it only needs to harden the spring or weaken the adhesion.
However, because the adhesion of the contact points is decided by the shape of the contact points, the material of the contact points, and the surface state, it is difficult to arbitrarily control the adhesion. Further, because the spring constant and the driving voltage of the switch have a trade-off relationship, the driving voltage is increased when the spring is hardened to reduce the return time. When the return time is long, the switching time is prolonged, and the performance of the switching switch is reduced.
As one way of overcoming such a problem, a method of separately placing an electrode for return to increase a return force has been known. For example, in Patent Literature 1, an electromechanical switch in which a signal transmission electrode fixed to a beam is in contact with a pair of lower signal transmission electrodes on the substrate when the beam is drawn toward a substrate direction with an electrostatic force is described. The electromechanical switch further includes fixed pectinate electrodes placed around the beam, and is configured to return the beam to the original position by generating an electrostatic force between the fixed pectinate electrodes and the beam.